Transmission of scheduling assignments in multiple operating bandwidths

ABSTRACT

Methods and apparatuses are described for the transmission of Scheduling Assignments (SAs) from a base station to User Equipments (UEs) for data reception in the downlink or data transmission in the uplink of a communication system consisting of multiple Component Carriers (CCs). The SAs are separately coded and transmitted using elementary units (Control Channel Elements or CCEs). Locations of CCEs determine whether an SA is intended for a first CC or for a second CC. Further, the location of CCEs for an SA intended for a first CC is used to determine locations of CCEs for an SA intended for a second CC.

PRIORITY

The present application is a continuation application of U.S. patentapplication Ser. No. 12/629,524, which was filed in the U.S. Patent andTrademark Office on Dec. 2, 2009, which claims priority under 35 U.S.C.§119(e) to U.S. Provisional Application No. 61/119,216, which was filedin the United States Patent and Trademark Office on Dec. 2, 2008, thecontent of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to wireless communicationsystems and, more specifically, to the transmission of control signalsconveying scheduling assignments for data reception or data transmissionin multiple distinct bandwidths of a communication system.

2. Description of the Art

Unicast communication systems consist of a DownLink (DL) and of anUpLink (UL). The DL conveys transmissions of signals from a serving BaseStation (BS or Node B) to User Equipments (UEs). The DL signals consistof data signals carrying the information content, control signals, andReference Signals (RS), which are also known as pilot signals. The datasignals are transmitted from the serving Node B to the respective UEsthrough the Physical Downlink Shared CHannel (PDSCH). The UL conveystransmissions of signals from UEs to their serving Node B. The ULsignals also consist of data signals, control signals, and RSs. The datasignals are transmitted from UEs to their serving Node B through thePhysical Uplink Shared CHannel (PUSCH).

A UE, which is also commonly referred to as a terminal or a mobilestation, may be fixed or mobile and may be a wireless device, a cellularphone, a personal computer device, etc. A Node B is generally a fixedstation and may also be referred to as a Base Transceiver System (BTS),an access point, or some other related terminology.

The DL control signals may be of broadcast or UE-specific (unicast)nature. Broadcast control signals convey system information to all UEs.Further, UE-specific control signals can be used, among other purposes,to provide to UEs Scheduling Assignments (SAs) for PDSCH reception (DLSAs) of PUSCH transmission (UL SAs). The transmission of UE-specificcontrol signals from the serving Node B to UEs is commonly through thePhysical Downlink Control CHannel (PDCCH). The UL control signalsinclude acknowledgement signals associated with the application ofHybrid Automatic Repeat reQuest (HARQ) for PDSCH transmissions andChannel Quality Indication (CQI) signals informing the serving Node B ofthe channel conditions the UE experiences in the DL. In the absence ofany data transmission, a UE transmits these control signals through thePhysical Uplink Control CHannel (PUCCH).

Typically, the PDCCH is a major part of the total DL overhead anddirectly impacts the achievable DL throughput. One method for reducingPDCCH overhead is to scale its size according to the resources requiredto transmit the SAs during each PDSCH Transmission Time Interval (TTI).In 3^(rd) Generation Partnership Project (3GPP) Long Term Evolution(LTE), where the Node B uses Orthogonal Frequency Division MultipleAccess (OFDMA) as the DL transmission method, a Control Channel FormatIndicator (CCFI) parameter transmitted through the Physical ControlFormat Indicator CHannel (PCFICH) indicates the number of OFDM symbolsoccupied by the PDCCH.

FIG. 1 illustrates the PDCCH transmission in the DL TTI, which forsimplicity, is assumed to consist of one sub-frame having M OFDMsymbols.

Referring to FIG. 1, the PDCCH 120 occupies the first N symbols of thetotal symbols 110. The remaining symbols 130 of the sub-frame areassumed to be primarily used for the PDSCH transmission. The PCFICH 140is transmitted in some sub-carriers, which are also referred to asResource Elements (REs), of the first symbol. Certain sub-frame symbolsalso contain RS REs 150 and 160 for each of the Node B transmitterantennas, respectively, which in FIG. 1 are assumed to be two. The mainpurposes of the RS are to enable a UE to obtain a channel estimate forits DL channel medium and to perform other measurements and functions.

Alternatively, additional control channels may also be transmitted inthe PDCCH region 120, even though they are not illustrated in FIG. 1.For example, assuming the use of HARQ for PUSCH data transmissions, aPhysical Hybrid-HARQ Indicator CHannel (PHICH) may be transmitted by theNode B in a similar manner as the PCFICH to indicate to groups of UEswhether or not their previous PUSCH transmission was correctly receivedby the Node B.

The Node B may separately code and transmit each of the DL SAs and ULSAs in the PDCCH.

FIG. 2 illustrates a processing chain for an SA coding.

Referring to FIG. 2, the SA information bits 210, which convey theinformation for PDSCH reception or PUSCH transmission to a UE, areappended Cyclic Redundancy Check (CRC) bits in step 220, and aresubsequently encoded in step 230, for example using a convolutionalcode, rate matched to the assigned resources in step 240, andtransmitted in step 250. Consequently, each UE performs multipledecoding operations in its respective PDCCH region to determine whetherit is assigned a DL SA or an UL SA. Typically, the CRC of each SA isscrambled with the IDentity (ID) of the UE the SA is intended for (notshown). After descrambling with its ID, a UE can determine whether an SAis intended for it by performing a CRC check.

In FIG. 3, the inverse operations of those illustrated in FIG. 2 areperformed for SA decoding at the UE receiver.

Referring to FIG. 3, the received SA 310, is rate de-matched in step320, decoded in step 330, and then the CRC is extracted in step 340.After CRC extraction, the SA information bits are obtained in step 350.As described above, if the CRC check passes, the UE may consider the SAas its own.

The SA information bits correspond to several fields such as, forexample, a Resource Allocation (RA) field indicating the part of theoperating BandWidth (BW) allocated to a UE for PDSCH reception (DL SA)or PUSCH transmission (UL SA), a Modulation and Coding Scheme (MCS)field, a field related to the HARQ operation, etc. Normally, the BW unitfor PDSCH or PUSCH transmissions consists of several REs, such as, forexample, 12 REs, and will be referred to herein as a Resource Block(RB).

In order to assist a UE with the multiple decoding operations, the REscarrying each SA are grouped into Control Channel Elements (CCEs) in thelogical domain. For a given number of SA bits in FIG. 2, the number ofCCEs for the SA transmission depends on the channel coding rate (e.g.,Quadrature Phase Shift Keying (QPSK) as the modulation scheme). For a UEwith low Signal-to-Interference and Noise Ratio (SINR), the serving NodeB may use a low channel coding rate for the respective SA transmissionin order to achieve a desired BLock Error Rate (BLER). For a UE withhigh SINR, the serving Node B may use a high channel coding rate for therespective SA transmission in order to achieve the same desired BLER.Therefore, the SA transmission to a UE experiencing a high SINR in theDL of the communication system typically requires more CCEs than thatthe SA transmission to a UE experiencing a low SINR (different powerboosting of the REs used for a CCE transmission may compensate to anextent for the difference in coding rates in order to achieve the sameSA BLER). Typical CCE aggregations for an SA transmission are assumed tofollow a “tree-based” structure consisting, for example, of 1, 2, 4, and8 CCEs.

For the SA decoding process, a UE may determine a search space forcandidate SAs, after it restores the CCEs in the logical domain (priorto CCE interleaving), according to a common set of CCEs for all UEs(UE-common search space) and a UE-specific set of CCEs (UE-specificsearch space). The UE-specific search space may be determined accordingto a pseudo-random function having as inputs UE-common parameters, suchas the sub-frame number or the total number of CCEs, and UE-specificparameters such as the identity assigned to a UE (UE_ID).

For example, in 3GPP LTE, for CCE aggregation levels Lε{1, 2, 4, 8}, theCCEs corresponding to SA candidate in are given by L·{(Y_(k)+m)mod└N_(CCE,k)/L┘}+i where N_(CCE,k) is the total number of CCEs insub-frame k, i=0, . . . , L−1, m=0, . . . , M^((L))−1, and M^((L)) isthe number of SA candidates to monitor in a search space (UE-common orUE-specific). Exemplary values of M^((L)) for Lε{1, 2, 4, 8} in theUE-specific search space are, respectively, {6, 6, 2, 2}. The variableY_(k) is defined as Y_(k)=(A·Y_(k-1))mod D, where Y⁻¹=UE_ID≠0, A=39827and D=65537.

FIG. 4 illustrates construction and transmission of SAs using CCEs.

Referring to FIG. 4, the CCEs are serially numbered in the logicaldomain 400. After channel coding and rate matching, as shown in FIG. 2,the encoded SA bits are mapped to CCEs in the logical domain. Morespecifically, the first 4 CCEs (L=4), CCE1 401, CCE2 402, CCE3 403, andCCE4 404 are used for the SA transmission to UE1. The next 2 CCEs (L=2),CCE5 411 and CCE6 412, are used for the SA transmission to UE2. The next2 CCEs (L=2), CCE7 421 and CCE8 422, are used for the SA transmission toUE3. Finally, the last CCE (L=1), CCE9 431, is used for the SAtransmission to UE4.

The SA bits may be scrambled in step 440 using binary scrambling code,which is typically cell-specific, and are subsequently modulated in step450. Each CCE is further divided into mini-CCEs. For example, a CCEconsisting of 36 REs can be divided into 9 mini-CCEs, each consisting of4 REs. Interleaving is applied among mini-CCEs (blocks of 4 QPSKsymbols) in step 460. For example, a block interleaver, as used in 3GPPLTE, may be used where the interleaving is performed onsymbol-quadruplets (4 QPSK symbols corresponding to the 4 REs of amini-CCE) instead of on individual bits.

After interleaving the mini-CCEs, the resulting series of QPSK symbolsmay be shifted by J symbols in step 470, and then each QPSK symbol ismapped to an RE in the PDCCH region of the DL sub-frame in step 480.

Accordingly, in addition to the RS from the two Node B transmitterantennas 491 and 492 and other control channels, such as the PCFICH 493and the PHICH (not shown), the REs in the PDCCH contain QPSK symbolscorresponding to the SAs for UE1 494, UE2 495, UE3 496, and UE4 497.

In order to support higher data rates and enable scheduling of signaltransmissions over BWs larger than the BWs of Component Carriers (CCs)supporting legacy communication systems, aggregation of multiple CCs istypically considered. For example, to support communication over 100MHz, aggregation of five 20 MHz CCs can be used. For ease of referenceherein, UEs operating over a single CC according to a pre-existingcommunication method will be referred to as “legacy-UEs” and UEsoperating over multiple CCs will be referred to as “advanced-UEs”.

Enabling the coexistence of SAs for legacy-UEs and advanced-UEs anddesigning the transmission of SAs for advanced-UEs are among thefundamental issues to be solved for the support of communications overmultiple CCs.

FIG. 5 illustrates the principle of CC aggregation.

Referring to FIG. 5, an operating BW of 100 MHz 510 is constructed bythe aggregation of 5 (contiguous, only for simplicity) CCs 521, 522,523, 524, and 525, each having a BW of 20 MHz. Similarly to thesub-frame structure for communication over a single CC in FIG. 1, thesub-frame structure for communication over multiple CCs consists of aPDCCH region, such as for example 531 through 535, and a PDSCH region,such as for example 541 and 545.

The PDCCH region size varies per CC and its value is signaled by thePCFICH in the respective CC for the reference sub-frame period. Byallowing the PDCCH to have a variable size, the respective overhead isminimized while practically avoiding PDSCH or PUSCH schedulingrestrictions. Additionally, by configuring an advanced-UE to receive itsPDSCH in predetermined CCs, the advanced-UE will only decode the PCFICHin these CCs and not all CCs, thereby minimizing the impact of PCFICHdecoding errors. For CCs 1 and 5, the PDCCH size is respectively,PDCCH-1=3 symbols 531 and PDCCH-5=1 symbol 535. Because the PDSCH sizein each CC is found by subtracting the respective PDCCH size from thesub-frame size, it is PDSCH-1=11 symbols 541 and PDSCH-5=13 symbols 545.

FIG. 5 also illustrates the direct extension of the PDCCH design for SAtransmissions to advanced-UEs. The scheduling is independent among CCsand is performed by a PDCCH that is included within its respective CC,regardless of the number of CCs an advanced-UE may use for its PDSCHreception or PUSCH transmission. For example, the advanced-UE 550receives two distinct SAs, SA2 552 and SA3 553, for individual PDSCHreception in the second and/or third CCs, respectively, and theadvanced-UE 560 receives SA5 565 for PDSCH reception in the fifth CC.Different transport blocks are associated with different SAs.

However, a disadvantage of using an individual SA in each CC is that theadvanced-UE will perform as many as 5 times (for the exemplary setup of5 CCs in FIG. 5) the number of decoding operations a legacy-UE has toperform in order to identify the SAs in all possible CCs.

Another design issue is the multiplexing of CCEs corresponding to SAsfor legacy-UEs and advanced-UEs without affecting the SA decodingprocess for legacy-UEs or increasing the number of decoding operationsfor advanced-UEs.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve at leastthe aforementioned problems in the prior art and the present inventionprovides methods and apparatus for the transmission of SchedulingAssignments (SAs) by a base station in multiple Component Carrier (CCs)of a communication system. The SAs provide scheduling information to aUser Equipment (UE) for Physical Downlink Shared CHannel (PDSCH)reception or Physical Uplink Shared CHannel (PUSCH). The SAs aretransmitted using Control Channel Elements (CCEs) in a Physical DownlinkControl CHannel (PDCCH).

An aspect of the present invention is to support scheduling of PDSCHreceptions or PUSCH transmissions in multiple CCs.

Another aspect of the present invention is to simplify and reduce the SAdecoding operations an advanced-UE performs.

Another aspect of the present invention is to improve the detectionreliability of SAs for advanced-UEs.

Another aspect of the present invention is to define the multiplexing ofCCEs for SAs corresponding to legacy-UEs and of CCEs for SAscorresponding to advanced-UEs, without affecting the SA decoding processof legacy-UEs.

In accordance with an aspect of the present invention, a logical domainlocation of CCEs for transmission of an SA to a UE in a first CCdetermines a logical domain location of CCEs for transmission of an SAto a same UE in a second CC.

In accordance with another aspect of the present invention, locations ofCCEs in a PDCCH determines whether an SA to a UE is intended to performPDSCH or PUSCH scheduling in a first CC or in a second CC.

In accordance with another aspect of the present invention, a CCindicator can be included in an SA to a UE to indicate whether the SA isintended to perform PDSCH or PUSCH scheduling in a first CC or in asecond CC.

In accordance with another aspect of the present invention, a number ofCCEs used for the SA transmission intended for a first CC determines anumber of CCEs used for the SA transmission intended for a second CC.

In accordance with another aspect of the present invention, a number ofcandidate SAs monitored by a UE configured multiple CCs in a searchspace is different than a number of candidate SAs monitored by a UEconfigured a single CC in a corresponding search space.

In accordance with another aspect of the present invention, locations ofCCEs in a logical domain for an SA to a UE that has been configured withmultiple CCs precedes locations of CCEs in the logical domain for an SAto a UE that has been configured with a single CC.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a conventional DL sub-frame structurefor PDCCH and PDSCH transmissions in a DL of a communication system;

FIG. 2 is a block diagram illustrating a conventional coding process ofan SA at a Node B;

FIG. 3 is a block diagram illustrating a conventional decoding processof an SA at a UE;

FIG. 4 is a diagram illustrating a conventional construction andtransmission of SAs using CCEs in a PDCCH;

FIG. 5 is a diagram illustrating a principle of component carrieraggregation;

FIG. 6 is a diagram illustrating a placement of CCEs for SA transmissionto advanced-UEs in multiple CCs and to legacy-UEs in a single CC inaccordance with an embodiment of the present invention;

FIG. 7 is a diagram illustrating a determination of CCEs at a UE thatare used to transmit SAs intended for a first CC and for a second CC inaccordance with an embodiment of the present invention;

FIG. 8 is a diagram illustrating a search and decode process at a UE fora DL SA intended for a second CC, after decoding a DL SA intended for afirst CC, in accordance with an embodiment of the present invention;

FIG. 9 is a diagram illustrating a search and decode process at a UE fora UL SA intended for a second CC, after decoding a UL SA intended for afirst CC, in accordance with an embodiment of the present invention;

FIG. 10 is a diagram illustrating a one-to-one mapping between a DL CCconveying a UL SA transmission and a UL CC of a respective PUSCHtransmission in accordance with an embodiment of the present invention;

FIG. 11 is a diagram illustrating a method for mapping a UL CC for PUSCHtransmission to a location of respective CCEs for a corresponding UL SAin accordance with an embodiment of the present invention; and

FIG. 12 is a diagram illustrating an explicit transmission of a DTXstate from a UE in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Certain embodiments of the present invention will be described morefully hereinafter with reference to the accompanying drawings. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the specific embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete and will fully convey the scope of thepresent invention to those skilled in the art.

Additionally, although the present invention is described in relation toan Orthogonal Frequency Division Multiple Access (OFDMA) communicationsystem, it also applies to all Frequency Division Multiplexing (FDM)systems in general and to Single-Carrier Frequency Division MultipleAccess (SC-FDMA), OFDM, FDMA, Discrete Fourier Transform (DFT)-spreadOFDM, DFT-spread OFDMA, SC-OFDMA, and SC-OFDM in particular.

In accordance with an embodiment of the present invention, anadvanced-UE is semi-statically configured with the CCs over which it mayhave PDSCH reception (DL CCs) or PUSCH transmission (UL CCs). Thetransmission of DL SAs and UL SAs to an advanced-UE is over theConfigured CCs (CCCs) of PDSCH reception and a different transport blockis associated with each DL SA or UL SA.

Each DL SA or each UL SA is transmitted from the Node B to anadvanced-UE in one DL CCC. The PDSCH reception associated with a DL SAmay be in the DL CCC of the DL SA transmission or it may be overmultiple DL CCCs addressed by the DL SAs. Correspondingly, the PUSCHreception associated with a UL SA may be in one UL CCC or it may be overmultiple UL CCCs addressed by the UL SAs. In order to associate a UL CCCwith the UL SA transmitted in a DL CCC, a one-to-one mapping can bepreconfigured between DL CCCs and UL CCCs, or an implicit ordering ofthe UL SAs can indicate the UL CCC, or explicit indexing can be includedin the UL SA to indicate the UL CCC for PUSCH transmission as it will belater described.

An advanced-UE can be configured with a primary DL CCC from among its DLCCCs. The primary DL CCC serves as reference relative to the remaining,secondary DL CCCs. For example, referring to FIG. 5, CC 2 may be theprimary DL CCC for an advanced-UE1 while CC 3 is a secondary DL CCC. Thesecondary DL CCCs may also be ordered, in which case, the DL CCCs can bereferred to as primary, first secondary, second secondary, etc.Equivalently, the DL CCCs for an advanced-UE may be ordered as first DLCCC, second DL CCC, etc., and a DL SA or an UL SA is transmitted in thefirst DL CCC. For simplicity, the “primary” and “secondary” terminologywill be used herein, but the terms “first”, “second”, etc., alsoapplies.

A search and decode process of DL SAs for an advanced-UE will now bedescribed below.

To maintain a similar number of decoding operations for an advanced-UEas for a legacy-UE and avoid disrupting the SA search and decode processof legacy-UEs, in accordance with an embodiment of the presentinvention, locations in a logical domain of CCEs for a DL SA to theadvanced-UE in secondary DL CCCs is determined from locations in thelogical domain of CCEs for a DL SA in a primary DL CCC. The CCEs formingthe DL SA candidates for an advanced-UE in each DL CCC can be treated insimilar fashion by the DL SA search and decode process as the CCEsforming the SA candidates for a legacy-UE. Moreover, as it issubsequently described, an advanced-UE can follow a DL SA search anddecode process with similar complexity as for a legacy-UE, regardless ofthe number of its DL CCCs, based on the condition that the locations ofthe CCEs for a DL SA in a secondary DL CCC are determined from thelocations of the CCEs for a DL SA in the primary DL CCC.

FIG. 6 is a diagram illustrating a placement of CCEs for SA transmissionto advanced-UEs in multiple CCs and to legacy-UEs in a single CC inaccordance with an embodiment of the present invention. Morespecifically, FIG. 6 illustrates five CCs as an example.

Referring to FIG. 6, a first CC 611 is configured to support onlylegacy-UEs, such as L-UE₁ 621, requiring 4 CCEs (1 through 4) for SAtransmission and L-UE_(K) 622, requiring 2 CCEs (K and K+1) for SAtransmission. The second and third CCs 612 and 613 support a mixture ofadvanced-UEs, such as A-UE₁, and legacy-UEs, such as L-UE_(L). A-UE₁ has2 DL CCCs. The primary DL CCC is CC 2 and the secondary DL CCC is CC 3.Four CCEs are required for the SA transmission to A-UE₁. The same CCEs 1through 4 are used in both the primary CCC 623 and the secondary CCC625. SAs to legacy-UEs are also transmitted in CC 2, such as the SA toL-UE_(L) using CCE L 624, and CC 3, such as the SA to L-UE_(M) using CCEM and M+1 626.

CC 4 614 also supports a mixture of advanced-UEs and legacy-UEs and CC 5615 supports only advanced-UEs. A-UE₂ also has 2 DL CCCs. The primary DLCCC is CC 4 and the secondary DL CCC is CC 5. For DL SA transmission toA-UE₂, two CCEs are used in the primary DL CCC 627 and one CCE is usedin the secondary DL CCC 629. More CCEs are used to provide better codingprotection for the DL SA transmission in the primary CCC because if theadvanced-UE fails to decode it, the decoding of the DL SAs in thesecondary DL CCCs will also fail, as the decoding of the DL SAs in thesecondary DL CCCs will occur only after the DL SA in the primary DL CCCis found and only the respective CCEs in the secondary DL CCCs areconsidered. After arranging the CCEs in each CC in the logical domain asdescribed above, the scrambling, modulation, interleaving, andRE-mapping process follows for each of CC 631, 632, 633, 634, and 635,as described above with reference to FIG. 4.

For each DL CCC, similar to a legacy-UE, an advanced-UE decodes thePCFICH to determine the respective PDCCH size and then performs thereverse functions of those illustrated in FIG. 4 by considering the REscarrying DL SA transmission for the DL SA search and decode process(that is, discarding predetermined REs carrying RS, PCFICH, PHICH, orpredetermined transmissions of other channels). Subsequently, theadvanced-UE de-interleaves, demodulates, and descrambles the REs toobtain the received CCEs. The DL SA search and decode process goesthrough the CCEs in the primary DL CCC.

Examples of CCE aggregation levels L for a DL SA transmission to eitherlegacy-UEs or advanced-UEs are 1, 2, 4, and 8 CCEs (Lε{1, 2, 4, 8}). Thelocations of CCEs for DL SA candidate m in the primary DL CCC aredetermined by the same function, L·{(Y_(k)+m)mod └N_(CCE,k)/L┘}+i aspreviously described, having the same arguments with the possibleexception of the total number of CCEs, N_(CCE,k), due to the possibledifferent PDCCH sizes in the CCCs. If the reference advanced-UE finds aDL SA in its primary DL CCC, it searches for additional DL SAs in thesecondary DL CCCs. Otherwise, the search and decode process terminatesin the primary DL CCC.

If there is more than one secondary DL CCC, semi-static or dynamicindexing may apply for indicating the series with which DL SAs areplaced in secondary DL CCCs, after the first DL SA in the primary DLCCC. For example, if in addition to its primary DL CCC an advanced-UE isconfigured with two secondary DL CCCs, the advanced-UE may besemi-statically configured through higher layers to search for a DL SAin the first secondary DL CCC before searching in the second secondaryDL CCC. If no DL SA is found in the first secondary DL CCC, the searchprocess may terminate.

Alternatively, an index may be included in the DL SA to indicate a nextDL CCC having a DL SA, if any, thereby allowing dynamic indexing on asub-frame basis. For example, for a total of 4 DL CCCs corresponding toone primary DL CCC and three secondary DL CCCs, a 2-bit index may beincluded in the DL SA to indicate the next secondary DL CCC having a DLSA (with a value of 0 indicating that no secondary DL CCC carries a DLSA).

Alternatively, a bit-map of 3 bits may be included in the DL SA in theprimary DL CCC to indicate which of the secondary DL CCCs have a DL SA.Nevertheless, using no indexing is also possible and, in that case, theadvanced-UE searches all secondary DL CCCs at the CCE locationsdetermined after successfully decoding a DL SA in the primary DL CCC.

FIG. 7 is a diagram illustrating a determination of CCEs at a UE thatare used to transmit SAs intended for a first CC and for a second CC inaccordance with an embodiment of the present invention.

Referring to FIG. 7, the reference advanced-UE is configured for DL SAreception in 2 CCs, its primary DL CCC 701 and a secondary DL CCC 702.Upon the signal reception in the primary DL CCC, the advanced-UE decodesthe PCFICH to determine the respective PDCCH region in step 711. Afterremoving REs used for the transmission of RS, PCFICH, PHICH and otherpredetermined channels in step 721, the advanced-UE restores acell-specific shift of J QPSK symbols, if any, in step 731,de-interleaves the mini-CCEs in step 741, and performs QPSK demodulationin step 751 to obtain the transmitted K CCEs CCE_(1,1), CCE_(2,1),CCE_(3,1), . . . , CCE_(K,1) in step 761.

After the CCEs have been restored in the logical domain, the second stepof the SA search and decode process determines search spaces in theprimary DL CCC according to a common set of CCEs for all UEs (UE-commonsearch space) and a UE-specific set of CCEs (UE-specific search space)as described above. If the advanced UE finds a DL SA in the primary DLCCC, it continues in the secondary DL CCC.

In the secondary DL CCC 702, similar to the primary DL CCC 701, theadvanced-UE decodes the PCFICH to determine the respective PDCCH regionin step 712. After removing REs used for the transmission of RS, PCFICH,PHICH and other predetermined channels in step 722, the advanced-UErestores a cell-specific shift of J QPSK symbols, if any, in step 732,de-interleaves the mini-CCEs in step 742, and performs QPSK demodulationin step 752 to obtain the transmitted M CCEs CCE_(1,2), CCE_(2,2),CCE_(3,2), . . . , CCE_(M,2) in step 762.

After the CCEs have been restored in the logical domain, the second stepof the DL SA search and decode process in the secondary DL CCCdetermines and decodes the candidate CCEs. This process is simpler thanin the primary DL CCC as the candidate CCEs in the secondary DL CCC canbe derived from the CCEs used by the DL SA in the primary DL CCC. Thatis, assuming that the DL SA in the primary DL CCC requires the same orbetter coding protection than the DL SA in a secondary CCE, aggregationlevels L smaller than or equal to the level used for the DL SA in theprimary DL CCC may be considered.

For example, if L=4 in the primary DL CCC, in the secondary DL CCCpossible values can be L=1, 2, 4. For L=1, 4 decoding operations areneeded (i.e., one decoding operation for each CCE). For L=2, 2 decodingoperations are needed (i.e., one for the first 2 CCEs, and one for thelast 2 CCEs). Finally, for L=4, 1 decoding operation is needed, whichbrings the total decoding operations to seven (7). Similarly, thelargest number of decoding operations is 15 and is obtained for L=8 inthe primary DL CCC and L=1, 2, 4, 8 in the secondary DL CCC. To minimizethe decoding operations, the same CCE aggregation level L may be used inall DL CCCs.

FIG. 8 is a diagram illustrating a search and decode process at a UE fora DL SA intended for a second CC, after decoding a DL SA intended for afirst CC, in accordance with an embodiment of the present invention.More specifically, FIG. 8 illustrates a search process in a secondary DLCCC, assuming that a reference advanced-UE detects a DL SA in a primaryDL CCC for L=4.

As described above, the CCEs considered by the search process in thesecondary DL CCC are deterministically known from the CCEs for the DL SAin the primary DL CCC. This can be achieved, for example, either byusing the same locations, or by applying a shift (for example, apredetermined shift depending on the PCFICH value in the secondary DLCCC), or by using a pseudo-random function, etc. Arguments (i.e.independent variables) to the pseudo-random function can be thesub-frame number, the CC number, the PCFICH value, and the UE_ID.

FIG. 8 assumes that possible CCE aggregation levels in a secondary DLCCC are equal to or greater than a CCE aggregation level used for a DLSA in a primary DL CCC. The first secondary DL CCC examined by thesearch process, after detecting a DL SA in the primary DL CCC, may besemi-statically or dynamically configured to the advanced-UE by itsserving Node B or it can be randomly chosen by the advanced-UE among thesecondary DL CCCs as it was previously described.

Referring to FIG. 8, after successfully decoding a DL SA in the primaryDL CCC, the advanced-UE continues in a secondary DL CCC 800 determinedby the indexing method, after completing the first step described inFIG. 7. In the secondary DL CCC, the advanced-UE considers only the CCEs810 determined from the CCEs used for the DL SA in the primary DL CCC.For simplicity, only the L=4 and L=2 CCE aggregation levels areconsidered. The L=8 and L=1 CCE aggregation levels can be addressed, ifneeded, in the same manner. Moreover, as previously described, the CCEaggregation level L in the secondary DL CCCs may be kept the same as inthe primary DL CCC (only one decoding operation will then be performedper secondary DL CCC).

In step 820, the advanced-UE first decodes the L=4 aggregation level. Ifthe decoding is successful in step 830, as indicated by the CRC test,the advanced-UE examines if the secondary DL CCC is the last DL CCC instep 832. If the secondary DL CCC is the last DL CCC, the search processfor DL SA terminates in step 834. However, if the secondary DL CCC isnot the last DL CCC, the search process for DL SAs continues for thenext secondary DL CCC in step 836.

If the decoding is not successful in step 830, another decoding isperformed considering the first 2 CCEs in step 840. If the decoding issuccessful in step 850, the advanced-UE examines if the secondary DL CCCis the last DL CCC in step 852. If the secondary DL CCC is the last DLCCC, the search process for DL SA terminates in step 854. However, ifthe secondary DL CCC is not the last DL CCC, the search processcontinues for the next secondary DL CCC in step 856.

If the decoding is not successful in step 850, another decoding isperformed considering the last 2 CCEs in step 860. If the decoding issuccessful in step 870, the advanced-UE examines if the secondary DL CCCis the last DL CCC in step 872. If the secondary DL CCC is the last DLCCC, the search process for DL SA terminates in step 874. However, ifthe secondary DL CCC is not the last DL CCC, the search processcontinues for a next secondary DL CCC in step 876.

If the decoding is not successful in step 870, the advanced-UEterminates the search process if the secondary DL CCC is either the lastone or, otherwise, it continues the search process for a next secondaryDL CCC in step 880. If more than one (1) CCE aggregation level isconsidered, the order with which the advanced-UE searches/decodes theseaggregation levels may be arbitrary. For example, in FIG. 8, the L=2 CCEaggregation level may be searched before the L=4 one.

For the transmission of UL SAs in accordance with an embodiment of thepresent invention, for a first UL SA, the CCEs are located in theprimary DL CCC and the same search process as for legacy-UEs applies(referred to as “a first approach”). The CCEs for all potential UL SAs,other than the first UL SA, are placed at predetermined locationsrelative to the CCEs for the first UL SA in the primary DL CCC. Forexample, the CCEs for UL SAs may be placed consecutive to the CCEs forthe first UL SA, or shifted by a predetermined number of CCEs (which maydepend on the PCFICH value in the primary DL CCC), or a pseudo-randommapping may apply.

For the transmission of UL SAs in accordance with another embodiment ofthe present invention, the UL SAs are distributed among the DL CCCs in asimilar manner as for the DL SAs using the same indexing options as forthe DL SAs where an UL CCC is associated with a DL CCC (referred to as“a second approach”). The locations of CCEs for UL SAs may follow thesame principles as applied for the locations of CCEs for DL SAs aspreviously described and illustrated in FIG. 8. Accordingly, thisdescription will not be repeated.

FIG. 9 is a diagram illustrating a search and decode process at a UE fora UL SA intended for a second CC, after decoding a UL SA intended for afirst CC, in accordance with an embodiment of the present invention.More specifically, FIG. 9 illustrates the first approach describedabove, assuming that no indexing is used for indicating UL CCCs withscheduled PUSCH transmission for an advanced-UE.

Referring to FIG. 9, after the advanced-UE successfully decodes thefirst UL SA 900, which is assumed to consist of L=4 CCEs 910, using thesame search and decode process as a legacy-UE, it examines predeterminedCCEs which may contain additional UL SAs. For simplicity, the CCEsallocated to UL SAs are assumed to be consecutive and potentialsubsequent UL SAs are assumed to comprise of either L=4 CCEs or L=2CCEs. Other CCE aggregation levels are also possible or the same CCEaggregation level may be used for all remaining UL SAs, if any. Thenext, second, and potential UL SA corresponding to the next UL CCCconsists of the next 4 CCEs 920.

If the decoding is successful in step 930, as indicated by the CRC test,the advanced-UE examines if the UL CCC is the last UL CCC in step 932.If the UL CCC is the last UL CCC, the search process terminates 934. Ifthe UL CCC is not the last UL CCC, the search process continues for anext UL CCC in step 936. However, if the decoding 930 is not successful,the next two (2) CCEs 940, after the CCEs used for the transmission ofthe first UL SA, are examined and correspond to the second UL CCC.

If the decoding is successful in step 950, the advanced-UE examines ifthe UL CCC is the last UL CCC in step 952. If the UL CCC is the last ULCCC, the search process terminates 954. However, if the UL CCC is notthe last UL CCC, the search process continues for a next UL CCC in step956.

If the decoding is not successful in step 950, the next two (2) CCEs960, after the CCEs used for the transmission of the first UL SA andafter the previous next two (2) CCEs, are examined.

If the decoding is successful in step 970, the advanced-UE examines ifthe UL CCC is the last UL CCC in step 972. If the UL CCC is the last ULCCC, the search process terminates in step 974. However, if the UL CCCis not the last UL CCC, the search process continues for a next UL CCCin step 976.

If the decoding is not successful in step 970, the UL SA search processeither terminates, if all UL CCCs are examined for all possible CCEaggregation levels assumed in FIG. 9, or otherwise, the UL SA searchprocess continues with additional CCE aggregation levels correspondingto the next UL CCC in step 980.

The above-described process assumes that the first UL SA corresponds tothe first UL CCC. Therefore, the first UL CCC will always have to bescheduled a PUSCH transmission. To avoid this restriction, the first ULSA may also contain an index for indicating the UL CCCs with valid ULSAs. This index, e.g., a number of bits, may either depend on the numberof UL CCCs a UE is configured with or it may be set to the total numberof UL CCCs.

For example, for four (4) UL CCCs, a bit-map including 4 bits in thefirst UL SA can indicate the UL CCCs for which the advanced-UE has an ULSA, with the first UL SA corresponding to the first such UL CCC. If theadvanced-UE is configured a smaller number of UL CCCs than the totalnumber of UL CCCs, the remaining bits in the bit-map can be set to apredetermined value or they can have a different interpretation, suchas, for example, for adjusting the resource used for subsequenttransmission of HARQ acknowledgement signals from the serving Node Bcorresponding to the respective PUSCH transmission from the advanced-UE.Alternatively, each UL SA can be allowed to address all UL CCCs at theexpense of additional bits required for the RA indication.

FIG. 10 is a diagram illustrating a one-to-one mapping between a DL CCconveying a UL SA transmission and a UL CC of a respective PUSCHtransmission in accordance with an embodiment of the present invention.More specifically, FIG. 10 illustrates the one-to-one mapping approachfor determining the UL CCC to which the respective UL SA refers toassuming that the RA field in each UL SA addresses only one UL CCC. Itis assumed that the second approach applies to the UL SA transmission,that is, UL SAs are transmitted in both the primary DL CCC and secondaryDL CCCs and that the UL CCCs are ordered.

Referring to FIG. 10, when an UL SA is successfully decoded in theprimary DL CCC 1010, the respective PUSCH transmission is in the firstUL CCC 1020; when an UL SA is successfully decoded in the firstsecondary DL CCC 1030, the respective PUSCH transmission is in thesecond UL CCC 1040; and when an UL SA is successfully decoded in theN-th secondary DL CCC 1070, the respective PUSCH transmission in the(N+1)-th UL CCC 1080.

It is not necessary for an UL SA to exist or be successfully decoded inan intermediate of the DL CCCs in order for the search process tocontinue until the final UL SA is successfully decoded. Instead, theadvanced-UE can simply continue the search process in subsequent DL CCCsmapped to respective UL CCCs. If the number of UL CCCs is larger thanthe number of DL CCCs, more than one UL CCCs are mapped to a DL CCC andthe order of the UL CCCs is determined by the order of the CCEs for therespective UL SAs.

For example, for two (2) DL CCCs and three (3) UL CCCs, the first andsecond UL CCCs can be respectively mapped to the first and second DLCCCs and the third UL CCC can be mapped to the first DL CCC. The firstand second approaches become equivalent if there is one DL CCC andmultiple UL CCCs.

FIG. 11 is a diagram illustrating a method for mapping a UL CC for PUSCHtransmission to a location of respective CCEs for a corresponding UL SAin accordance with an embodiment of the present invention. Morespecifically, FIG. 11 illustrates an implicit mapping approach, based oneach UL SA location, for determining the UL CCC to which the respectiveUL SA refers to. It is assumed that all UL SAs are transmitted usingsequential CCEs, in the logical domain, in the primary DL CCC and eachUL SA addresses only one UL CCC. Clearly, if the UL SAs are transmittedin different DL CCCs as assumed for the one-to-one mapping approach, theone-to-one mapping and implicit mapping approaches are equivalent andthe description in FIG. 10 applies.

Referring to FIG. 11, the first UL SA in the primary DL CCC 1110 mapsthe respective PUSCH transmission in the first UL CCC 1120; the secondUL SA in the primary DL CCC 1130 maps the respective PUSCH transmissionin the second UL CCC 1140; and the N-th UL SA in the primary DL CCC 1170maps the respective PUSCH transmission in the N-th UL CCC 1180. Withexplicit mapping, the UL CCCs can be signaled in each UL SA.

For example, four (4) UL CCCs can be addressed with 2 bits in each ULSA, e.g., ‘00’ maps to the first UL CCC, ‘01’ maps to the second UL CCC,‘10’ maps to the third UL CCC, and ‘11’ maps to the fourth UL CCC. TheUL SAs may be in the primary DL CCC or they may also be located insecondary DL CCCs, either through a predetermined mapping or randomlywithout any restrictions.

Alternatively, a bit-map may be used in the UL SA in the primary DL CCCto indicate the UL CCCs for which an UL SA is transmitted using one ofthe previously described mapping approaches. Explicit mapping of the ULCCCs can be avoided by extending the RA field in each UL SA to addressthe RBs in all UL CCCs.

The explicit mapping approach can also apply for the DL SAs and forscheduling HARQ re-transmissions. If each DL SA can only address one DLCCC, this DL CCC can be identified through explicit signaling.

For example, the DL SA may be transmitted in the primary DL CCC but therespective PDSCH transmission may be in a secondary DL CCC, which isidentified through explicit mapping bits, which address the DL CCCs, inthe DL SA. Therefore, if a HARQ re-transmission is to be scheduled in asecondary DL CCC, the respective DL SA can be transmitted in the primaryDL CCC, even when there is no PDSCH transmission scheduled for thereference advanced-UE in the primary DL CCC.

An advanced-UE may also be scheduled multiple PDSCH receptions ormultiple PUSCH transmissions in the same DL CCC or UL CCC, respectively.

For example, a first PDSCH reception may correspond to a Voice overInternet Protocol (VoIP) packet while a second PDSCH reception maycorrespond to the download of a data file. These PDSCH receptions orPUSCH transmissions may be scheduled using the same or using differentformats for the respective DL SAs or UL SAs. The advanced-UE may bepre-configured for such behavior and the search and decode process ismodified to account for the multiple DL SAs or multiple UL SAs. Forexample, a separate search and decode process may apply for each of thedifferent DL SAs or UL SAs formats.

For the Lε{1, 2, 4, 8} CCE aggregation levels, different values of M⁽¹⁾,M⁽²⁾, M⁽⁴⁾, and M⁽⁸⁾ may be used for legacy-UEs and advanced-UEs. Onereason may be that advanced-UEs may be fewer and can be alwaysconfigured to operate as legacy-UEs if the conditions required forsupporting transmission at higher data rates and over larger BWs(multiple CCs) are not satisfied. Moreover, even when many advanced-UEsexist in a system, such UEs typically experience high SINRs so that thelarger CCE aggregations for respective SA transmissions are less likelythan for legacy-UEs, and therefore, the SA candidates for advanced-UEsfor the larger (or smaller) CCE aggregation levels should be less (ormore) than the ones for legacy-UEs.

In order to minimize the PDCCH size in each CC, the CCEs for SAs toadvanced-UEs may be placed with priority in the logical domain beforethe CCEs for SAs to legacy-UEs as illustrated in FIG. 6. Otherwise,because the number of SAs to legacy UEs may be different among the CCs,in order to maintain the same location of CCEs among primary andsecondary DL CCCs for SAs to advanced-UEs, CCEs used for SAs to legacyin one CC may remain empty in another CC, thereby unnecessarilyincreasing the PDCCH size in the latter CC.

In order to improve interference randomization for the SA transmissionto an advanced-UE and statistically average PDCCH loading among the DLCCCs, the primary DL CCC an advanced-UE is configured maypseudo-randomly vary among all DL CCCs. In accordance with an embodimentof the present invention, the pseudo-random function has bothUE-specific parameters as inputs, such as the identity assigned to a UE(UE_ID) or a total number C of DL CCCs an advanced-UE is configuredwith, and UE-common parameters, such as a sub-frame number k. Theprimary DL CCC in sub-frame k, c_(P,k), can be determined asC_(P,k)=Z_(k) mod C where Y_(k)=(A·Y_(k-1))mod D where Z⁻¹=UE_ID≠0,A=39827 and D=65537. Less frequent variation of the primary DL CCC mayalso apply. For example, the variation may be per frame (a frame isassumed to consist of 10 sub-frames) and in that case, k denotes theframe number.

By informing an advanced-UE of the DL CCCs it has a scheduled PDSCHreception with or of the UL CCCs it has a scheduled PUSCH transmissionwith, the advanced-UE becomes aware when it fails to detect therespective DL SA or UL SA. As previously described, such information maybe conveyed through explicit signaling in the first DL SA or the firstUL SA, respectively, which the advanced-UE is assumed to successfullydecode.

When the advanced-UE knows it has been assigned an additional DL SA, butthe decoding fails, it can explicitly transmit a discontinuoustransmission (DTX) signal instead of a positive or negative HARQacknowledgement signal, ACK or NAK respectively, as there is no PDSCHreception. When the ACK/NAK transmission is in the PUCCH, another statecan be applied to the signal transmission to represent DTX. When theACK/NAK transmission is in the PUSCH, the advanced-UE may assist itsserving Node B with the DTX detection by transmitting, for example, aseries of {+1, −1} bits, or in general, a series of opposite values, inthe resources reserved for ACK/NAK transmission in the PUSCH.

FIG. 12 is a diagram illustrating an explicit transmission of a DTXstate from a UE in accordance with an embodiment of the presentinvention. More specifically, FIG. 12 illustrates an explicit DTXtransmission in the PUCCH from a UE for missed DL SAs, other than thefirst DL SA. The values used for the ACK, NAK, and DTX are merelyprovided as an example.

Referring to FIG. 12, considering 1-bit ACK/NAK transmission, theconventional approach assumes that the UE transmits either a NAK 1210 oran ACK 1220 to indicate the incorrect or correct PDSCH reception,respectively. However, in accordance with an embodiment of the presentinvention, when the UE is aware of a DL SA that it fails to decode, theDTX state 1230 is introduced in the ACK/NAK signal transmission. Thesame applies in case a 2-bit ACK/NAK transmission is expected by theserving Node B, where a value of ‘1’ may represent {NAK, NAK}, a valueof T may represent {NAK, ACK}, a value of ‘−1’ may represent “ACK, ACK”and a value of ‘−j’ may represent {ACK, NAK}.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims.

What is claimed is:
 1. A method for transmitting a plurality ofScheduling Assignments (SA) through a downlink control channel by a NodeB in a wireless communication system supporting carrier aggregation, themethod comprising the steps of: transmitting to a User Equipment (UE) afirst SA intended for a first Component Carrier (CC) using a first setof Control Channel Elements (CCEs); and transmitting to the UE a secondSA intended for a second CC using a second set of CCEs, wherein alocation of the second set of CCEs is determined from a location of thefirst set of CCEs, and wherein a location of a first CCE included in thesecond set of CCEs is shifted by a predetermined number of CCEs relativeto a location of a first CCE included in the first set of CCEs, andwherein the location of the first CCE included in the second set ofCCEs, shifted from the location of the first CCE included in the firstset of CCEs, is determined by using a CC indicator.
 2. The method ofclaim 1, wherein the UE is configured with the first CC and the secondCC from among multiple CCs.
 3. The method of claim 2, wherein the firstCC is a primary CC that is configured to the UE and the second CC is asecondary CC which is able to be configured to the UE.
 4. An apparatusfor transmitting a plurality of Scheduling Assignments (SA) through adownlink control channel by a Node B in a wireless communication systemsupporting carrier aggregation, the apparatus comprising: a transmitterfor transmitting an SA to a User Equipment (UE); and a controller forcontrolling operations of transmitting to the LIE a first SA intendedfor a first Component Carrier (CC) using a first set of Control ChannelElements (CCEs), and transmitting to the UE a second SA intended for asecond CC using a second set of CCEs, wherein a location of the secondset of CCEs is determined from a location of the first set of CCEs,wherein a location of a first CCE included in the second set of CCEs isshifted by a predetermined number of CCEs relative to a location of afirst CCE included in the first set of CCEs, and wherein the location ofthe first CCE included in the second set of CCEs, shifted from thelocation of the first CCE included in the first set of CCEs, isdetermined by using a CC indicator.
 5. The apparatus of claim 4, whereinthe UE is configured with the first CC and the second CC from amongmultiple CCs.
 6. The apparatus of claim 5, wherein the first CC is aprimary CC that is configured to the UE and the second CC is a secondaryCC which is able to be configured to the UE.
 7. A method for searching aplurality of Scheduling Assignments (SA) through a downlink controlchannel by a User Equipment (UE) in a wireless communication systemsupporting carrier aggregation, the method comprising the steps of:searching a first SA, intended for a first Component Carrier (CC),transmitted from a Node B by using a first set of Control ChannelElements (CCEs); and searching a second SA, intended for a second CC,transmitted from the Node B by using a second set of CCEs, wherein alocation of the second set of CCEs is determined from the location ofthe first set of CCEs, wherein a location of a first CCE included in thesecond set of CCEs is shifted by a predetermined number of CCEs relativeto a location of a first CCE included in the first set of CCEs, andwherein the location of the first CCE included in the second set ofCCEs, shifted from the location of the first CCE included in the firstset of CCEs, is determined by using a CC indicator.
 8. The method ofclaim 7, wherein the UE is configured with the first CC and the secondCC from among multiple CCs.
 9. The method of claim 8, wherein the firstCC is a primary CC that is configured to the UE and the second CC is asecondary CC which is able to be configured to the UE.
 10. A UserEquipment (UE) for searching a plurality of Scheduling Assignments (SA)through a downlink control channel in a wireless communication systemsupporting carrier aggregation, the UE comprising: a receiver forreceiving a signal from a Node B; and a controller for controllingoperations of searching a first SA, intended for a first ComponentCarrier (CC), transmitted from the Node B by using a first set ofControl Channel Elements (CCEs), and searching a second SA, intended fora second CC, transmitted from the Node B by using a second set of CCEs,wherein a location of the second set of CCEs is determined from thelocation of the first set of CCEs, wherein a location of a first CCEincluded in the second set of CCEs is shifted by a predetermined numberof CCEs relative to a location of a first CCE included in the first setof CCEs, and wherein the location of the first CCE included in thesecond set of CCEs, shifted from the location of the first CCE includedin the first set of CCEs, is determined by using a CC indicator.
 11. TheUE of claim 10, wherein the UE is configured with the first CC and thesecond CC from among multiple CCs.
 12. The UE of claim 11, wherein thefirst CC is a primary CC that is configured to the UE and the second CCis a secondary CC which is able to be configured to the UE.